The Shay, Part 5: The Crankshaft, Take 5

You are at liberty to call me insane (I've been called far worse). After the failure of attempt number 4, I was prepared to backpedal a little to return to the "safer" territory of heavier materials. But instead, I awoke this Sunday morning feeling just a bit adventurous. I simply didn't like the idea of going fatter; in fact, I decided to go thinner!

Granted, I couldn't hope to approach close-to-scale, let alone exact scale—the smallest parts I've been able to make so far have been nearly 100% too large. The best I could possibly achieve would be something that merely looked fine enough to be correct. The critical dimensions are thicknesses and spacing: the fatter the web parts, the longer the crankshaft becomes. So, sticking with .012-inch thick sheet metal for the webs puts me within 10% of scale for that one important dimension.

The other issue has been the crankshaft diameter. Up to now I've been reluctant to drop from .020-inch diameter steel wire—which scales up to a whopping 4.4 inches—to .015-inch diameter wire, a more believable 3.3 scale inches. The thicker wire forces the webs to be grossly oversized, so I just needed to get over my reluctance and make the switch. What helped push me over the edge was a marvelous clinic on drilling tiny holes by Tony Sissons.

The first thing I did was drill a test hole with a #79 bit in a scrap if .012-inch thick nickel silver sheet (below left), just to get a feel for a process I'd be repeating a great many times—it seemed to take forever. It was a bit too snug for the wire, which meant that, as before, I'd re-drill with a #78 bit after cutting the parts out. While this may sound redundant, it improves the alignment of hole pairs, as the re-drilling is done when they're sandwiched together.

Then I started drilling. And drilling and drilling. (A popular phrase comes to mind here that I refuse to utter.) Not all hole pairs were useful, so I had to keep drilling; plus, I wanted plenty of spares. I stopped at 28, after having broken two bits (above right). I was surprised to find that the bits seemed to get dull quickly; I suspect they weren't the best of quality.

After slicing the hole pairs out of the sheet with a jeweler's saw (above left), I started the process of grinding them down to size. For this step, I returned to my old ways of holding the parts in my fingers rather than with a tool (above right): it allows me to feel the part as it's being ground, which helps me control the process better, in spite of my increasing shakiness—tools seem to make things worse. I also didn't count parts; I just kept on grinding until I ran out of pieces, so I had a wide array from which to choose the best, plus a nice supply of spares.

I reached something of a tipping point, however, as I began soldering the cranks together. I was using a .015-inch thick spacer, instead of a .020-inch one as before (above left, compared to a ballpoint pen tip), and I started to question my decision to go down this path. Even if I was able to complete the crankshaft, surely I wasn't going to be able to make it functional! This consideration struck me as I was staring at a crankpin that measured .015 by .015 inches, and covered with silver solder that I'd have to somehow remove (above right). Would I be able to do that?

Then, for a brief moment I contemplated abandoning the project altogether, and perhaps switching to HOn3. But I imagine the thought of giving up has passed through the mind of almost anyone deep in the throes of attempting to achieve an extremely challenging goal. Indeed, I've been through this several times myself before; I simply needed to press on.

Yet another "that's it, I'm giving up" moment came as I soldered the last crank assembly to the crankshaft—it completely flooded with solder. As I sat staring at the silver blob that was supposed to be a crank, I was eventually reminded of my first attempt to make a Shay crankshaft: at one point, the whole thing was just a lumpy glob, and I just picked at it with grinding discs and files and knives until I got down to the core parts. So I shrugged off this bump in the road and pressed on again.

As it happens, I was able to remove the excess solder from the crank pins after all, thanks to a mistake I'd made early on: I thought I could cut through steel music wire with a jeweler's saw. Puh. All it did was polish the wire. Eureka! With my trusty jeweler's saw I soon had all of the crank pins gleaming like new. I also made my own filing tools by attaching narrow strips of ultra-fine sanding film to the sides of needle files. It took a painfully long time, but eventually I extracted a finished crankshaft out of a hopeless-looking mess.

At the end of the day, I wasn't exactly thrilled by what I'd produced: it was about as crude as my first one. But I had to remind myself that this one was 20-25% smaller than my "personal best" so far. Should I make another one to further refine it? Why the hell not?

Continue to Part 6
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